		var canvas = document.getElementById("canvas"),
	              context = canvas.getContext("2d");
	        	  video = document.getElementById("video");

        // Put event listeners into place
       window.addEventListener("DOMContentLoaded", function() {
            // Grab elements, create settings, etc.
           /*  var canvas = document.getElementById("canvas"),
                context = canvas.getContext("2d"), //getContext唯一合法值2d
                video = document.getElementById("video"), */
                videoObj = {
                    "video": true,
                    "audio": true
                },
                errBack = function(error) {
                    console.log("Video capture error: ", error.code);
                };

            // Put video listeners into place
            //navigator.getUserMedia =  navigator.getUserMedia || navigator.webkitGetUserMedia || navigator.mozGetUserMedia;
            if (navigator.getUserMedia) { // Standard 如果用户允许打开摄像头
                //stream为读取的视频流
                navigator.getUserMedia(videoObj, function(stream) {
                    video.src = stream;
                   
                    video.play();
                }, errBack);
            } else if (navigator.webkitGetUserMedia) { // WebKit-prefixed  根据不同的浏览器写法不同
                navigator.webkitGetUserMedia(videoObj, function(stream) {
                    video.src = window.webkitURL.createObjectURL(stream);
                   
                    video.play();
                }, errBack);
            } else if (navigator.mozGetUserMedia) { // Firefox-prefixed
                navigator.mozGetUserMedia(videoObj, function(stream) {
                    video.src = window.URL.createObjectURL(stream);
                  
                    video.play();
                }, errBack);
            }
            
        }, true);
